Powder coating is a wonderful way to apply a smooth, colored surface to a part, whether for aesthetic reasons or corrosion protection. Traditionally, powder is applied via a air gun that sprays it towards a part while giving the grains an electrostatic charge. The part to be coated (generally metal) is hanging on a rack and given an opposite charge, and the powder readily flows to the surface and sticks well. The dry coated part is then placed in an oven which melts the powder into a solid, continuous surface. The main drawback of the process is that while simple parts with large surfaces are easy to coat, it can become difficult to get powder to flow evenly into deep crevices, or inside a hollow part such as a tube.
Enter fluidized bed powder coating — a process in which air shoots through a vat of powder, making it move like a fluid. A heated part can be dipped inside the vat, instantly melting a thin layer of powder around the part. This much simpler method is great at getting inside all those pesky crevices that traditional coating can’t touch, and hacker [Amper] was able to build a custom fluidized bed coater in a Pringles can. This rendition, inspired by this video tour of Dan Gelbart’s workshop, uses a coffee filter to evenly distribute the air flow supplied by a small compressor — [Amper] quickly learned that just sticking a tube in a bucket of powder results in more of a volcano than a nice, fluid surface. A burner heated up some pieces of metal that were then dipped them in the can, resulting in complete coverage, even inside the tiny 5 mm diameter hole down the center of a piece of 80/20 extrusion. Once [Amper] got the basic idea working, the idea scaled up into a larger machine that you can check out in the video below.
There’s no beating the beauty and durability of a high-quality powder-coated part. There’s just something about the look and feel of the finish that goes far beyond mere painting and makes it worth the effort and expense. The typical electrostatic spray powder-coating setup can be expensive, though, and not necessarily suitable for every workpiece.
Enter the fluidized-bed powder coating chamber, perfect for limited runs of small parts, and the brainchild of [Andrew Mayhall]. With a business providing furniture kits based on iron pipe, [Andrew] needed a way to finish flanges and fittings, and powder coating provided the best look. The fluidizer he built is a great alternative to spray coating; it blows air through a bed of fine thermoplastic granules, which causes them to act like a fluid. It’s similar to the fluidized-bed hot tub we recently featured, but on a much smaller scale and with different requirements based on the ultrafine particle size and aggregation properties of the powder. [Andrew] had to add mechanical agitation to achieve a homogeneous fluid bed, and after much experimentation he’s now able to dip preheated parts into the bed and achieve one-step powder coating. The video after the break shows some of the operational details.
We’ll preface this by stating that this isn’t the easiest hack to pull off on a lazy Saturday afternoon. You need a spare hot tub, plenty of pipe, and a seriously big air supply. But if you can pull it all together, the payoff is fantastic.
What [Mark] has achieved is turning a regular hot tub into a fluidized bed. In simple terms, this is where a solid particulate material (like sand) is made to act more like a fluid by passing pressurized fluid through the material. Through a carefully built series of drilled copper pipes, [Mark] manages to turn the hot tub into a fluidized bed, much to the enjoyment of his young nephews.
While it’s not the easiest hack to copy at home, [Mark] drives home the science of both the fluidized bed and why certain objects float or sink in the sand. It’s something that can also be easily tackled at a smaller scale, if you’re looking for something more achievable for the average maker.